The White House has denied preventing the CIA director, Gina Haspel, from briefing the Senate on the murder of Saudi dissident and Washington Post columnist, Jamal Khashoggi.

The secretary of state, Mike Pompeo, and the defence secretary, James Mattis, are due to give a briefing on US relations with Saudi Arabia to the entire Senate behind closed doors on Wednesday, ahead of a vote that could cut off US support for Riyadh’s military campaign in Yemen.

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On a national security issue of such importance, it would be customary for a senior intelligence official to take part, Senate staffers said. On this occasion, the absence of the intelligence community is all the more glaring, as Haspel travelled to Istanbul to hear audio tapes of Khashoggi’s murder provided by Turkish intelligence, and then briefed Donald Trump.

Senior senators – including the chairman of the foreign relations committee, Bob Corker – have called for Haspel to appear, but there was no sign on Tuesday evening that she will take part.

Officials said that the decision for Haspel not to appear in front of the committee came from the White House, but the national security adviser, John Bolton, denied it. “Certainly not,” he told reporters, but left it unclear why there would be no intelligence presence.

The US president has asserted, however, that the CIA report is inconclusive. He told the Washington Post on Tuesday: “Maybe he did and maybe he didn’t. But he denies it. And people around him deny it … I’m not saying that they’re saying he didn’t do it, but they didn’t say it affirmatively.”

Trump’s faith in the crown prince is treated with profound scepticism by many senators who expected to hear first-hand from Haspel on Wednesday on a brutal killing that appears to have help sway several senators against continuing military support to Riyadh for the war in Yemen.

That conflict is thought to have killed more than 50,000 people, with many of the casualties coming from the Saudi-led coalition’s aerial bombing campaign. The coalition’s use of economic blockades has meanwhile help bring the country to the brink of famine. Save the Children estimates that up to 85,000 children have died of hunger.

Against that backdrop the administration is increasingly nervous that the Senate will rebel against its policy of maintaining support for Riyadh and Prince Mohammed, asserting its powers under the War Powers Resolution.

As of Tuesday, however, the Senate was told by the administration to expect only Pompeo and Mattis at the Wednesday briefing. The White House did not respond to a query on the absence of an intelligence official.

“There is always an intel person there for a briefing like this,” a Senate staffer told the Guardian. “It is totally unprecedented and should be interpreted as nothing less than the Trump administration trying to silence the intelligence community.”

“This is further evidence that the White House is trying to outdo the Saudis in carrying out the worst cover-up in modern history,” Riedel added.

Bolton told reporters on Tuesday that he had not heard the tape of Khashoggi’s murder, and did not intend to.

“People who speak Arabic have listened to the tape and given us the substance of what’s in it,” Bolton said a White House briefing. Pressed on why he had not listened to something of such potential importance to relations with Riyadh, he retorted: “How many of you speak Arabic? I guess I should ask you why you think I should [listen]? What do you think I would learn from it?”

A previous attempt to cut off military assistance to Riyadh under the War Powers Resolution, sponsored by the independent senator Bernie Sanders, Democrat Chris Murphy and Republican Mike Lee, was blocked in March this year by a 55-44 margin.

But several senators who voted to shelve the resolution then have since changed their mind, including Bob Menendez, the top Democrat on the Senate foreign relations committee, and Corker.

Both senators have called for the administration to make a formal judgment on Prince Mohammed’s involvement in the Khashoggi murder and renewed calls for Haspel to appear on Wednesday.

“The briefings are lacking because there’s no one from the intelligence community there. That says to me that you are specifically trying not to have the key question asked,” Menendez said on Monday according to DefenseNews.

“I’ve laid in the railroad tracks in the past to keep us from blocking arms to Saudi Arabia,” Corker told reporters. “I’m in a real different place right now as it relates to Saudi Arabia.”

The timing of the vote on the Saudi resolution is unclear. Sanders has said there is support for holding it this week. The Republican majority leader in the Senate, Mitch McConnell, can try to postpone it, but cannot put it off indefinitely, as any measure under the War Powers Resolution has privileged status and cannot be stopped from going to the Senate floor for a vote.